Method for stabilizing lipf6, electrolyte solution for nonaqueous secondary batteries having excellent thermal stability, and nonaqueous secondary battery having excellent thermal stability

A nonaqueous electrolyte solution comprising LiPF6 as an electrolyte and a cyclic carbonate and/or a chain carbonate as a solvent, and a phosphoric acid ester amide represented by the following general formula (I) in such an amount that a molar ratio of the phosphoric acid ester amide with respect to LiPF6 is 0.001 to 2:

• where:
• m is 1 or 2;
• each of R1 and R2 represents a branched or linear alkyl group comprising 1 to 6 carbon atoms and/or a hydrocarbon group comprising an unsaturated bond, wherein R1 and R2 optionally comprise a substituent that is selected from the group consisting of an alkoxy group, an amino group, an alkylthio group, a saturated heterocyclic group, an unsaturated heterocyclic group, and a fluorine atom, and wherein R1 and R2 optionally combine together to form a 5 to 8 membered cyclic structure;
• and
• R3 represents a branched or linear alkyl group comprising 1 to 6 carbon atoms or a branched or linear fluorine-containing alkyl group comprising 1 to 6 carbon atoms.

A nonaqueous secondary battery comprising a positive electrode and a negative electrode that are capable of occluding and releasing lithium, a separator, an electrolyte solution comprising LiPF6 as an electrolyte and a cyclic carbonate and/or a chain carbonate as a solvent and a phosphoric acid ester amide represented by the following general formula (I) in such an amount that a molar ratio of the phosphoric acid ester amide with respect to LiPF6 is 0.001 to 2:

• where:
• m is 1 or 2;
• each of R1 and R2 represents a branched or linear alkyl group comprising 1 to 6 carbon atoms and/or a hydrocarbon group comprising an unsaturated bond, wherein R1 and R2 optionally comprise a substituent that is selected from the group consisting of an alkoxy group, an amino group, an alkylthio group, a saturated heterocyclic group, an unsaturated heterocyclic group, and a fluorine atom, and wherein R1 and R2 optionally combine together to form a 5 to 8 membered cyclic structure;
• and
• R3 represents a branched or linear alkyl group comprising 1 to 6 carbon atoms or a branched or linear fluorine-containing alkyl group comprising 1 to 6 carbon atoms.